Protoplanetary discs around sun-like stars appear to live longer when the metallicity is low

TL;DR

This study uses JWST spectroscopy to analyze pre-main sequence stars in the metal-poor SMC, revealing that circumstellar discs around these stars may have longer lifespans in low-metallicity environments, challenging previous assumptions.

Contribution

First spectroscopic confirmation of PMS stars in the SMC showing long-lived discs, highlighting the impact of low metallicity on disc longevity.

Findings

PMS stars in the SMC are still accreting gas after 10 Myr.

Spectra show near-infrared excess and H2 lines indicating discs.

Discs around low-metallicity stars may persist longer than in metal-rich environments.

Abstract

Previous Hubble Space Telescope (HST) observations of the star-forming cluster NGC 346 in the Small Magellanic Cloud (SMC) had revealed a large population of pre-main sequence (PMS) candidates, characterised by Halpha excess emission in their photometry. However, without access to spectroscopy, the nature of these objects remained unclear. Using the NIRSpec instrument on board JWST, we studied a sample of these stars, with masses in the range ~0.9-1.8 Msun, effective temperatures in the range 4,500-8,000 K, and PMS ages between ~0.1 and 30 Myr. Here we present the first spectra of solar-mass PMS stars in the metal-poor SMC (Z=1/8 Zsun) and discuss the physical properties of ten representative sources with good signal-to-noise ratio. The observations indicate that even the oldest of these PMS candidates are still accreting gas with typical rates of ~10^{-8} Msun/yr for stars older than ~10 Myr, confirming their PMS nature. The spectra also reveal near-infrared excess and molecular hydrogen excitation lines consistent with the presence of discs around these stars. These findings suggest that in a low-metallicity environment circumstellar discs can live longer than previously thought.